如何验证此 Java 代码的用户输入？

Question

我想要验证：仅输入数字，小时必须

 int total; //Total Minutes
    String time; //Input from keyboard


    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    //Get the value before the ':'
    int hour = Integer.parseInt(time.substring(0, time.indexOf(':')));


    //Get the value after the ':'
    int minute =Integer.parseInt (time.substring((time.indexOf(':') + 1), time.length()));


    //Formula of the calculation
    total = hour * 60 + minute;


    //Display the final value
    System.out.println( time +" is " + total + " minutes.");

Answer 1

为了验证，使用正则表达式：

time.matches( "(?:[01][0-9]|2[0-3]):[0-5][0-9]" )

要转换，只需使用

int hour = Integer.parseInt(time.substring(0, 2));
int minute = Integer.parseInt(time.substring(3));

Answer 2

要遵循您的格式，用户必须在第三个字符位置charAt(2) 处输入带有“:”的时间，并且其余字符（在索引 0、1、3 和 4 处）必须是数字。一个快速实施且易于学习的解决方案是使用正则表达式：http://www.regular-expressions.info/tutorial.html

不过，我将向您展示一个使用您的代码作为模板的更易于理解的解决方案：

1. 验证长度为5
2. 验证时间是否正确
3. 验证分钟数是否正确
4. 如果有任何错误，请用户重新输入值

代码如下：

    int total; // Total Minutes
    String time; // Input from keyboard

    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    boolean correctFormat = false;
    int hour = 0, minute = 0;

    while (!correctFormat) {
        correctFormat = true;

        if (time.length() != 5)
            correctFormat = false;
        else {

            // Get the value before the ':'
            hour = Integer.parseInt(time.substring(0, 2));
            if (hour >= 24 || hour < 0)
                correctFormat = false;

            // Get the value after the ':'
            minute = Integer.parseInt(time.substring(3, 5));
            if (minute >= 60 || minute < 0)
                correctFormat = false;
        }
        if (!correctFormat) {
            System.out.print("Pleaase follow the format! Enter the time in HH:MM :");
            time = T.next();
        }

    }

    // Formula of the calculation
    total = hour * 60 + minute;

    // Display the final value
    System.out.println(time + " is " + total + " minutes.");

此外，如果您想让代码更加健壮，您可以通过捕获将由Integer.parseInt() 方法抛出的“NumberFormatException”来检查用户是否在“:”之前和之后输入了数字如果参数不是实际数字。您可以通过将上面的代码编辑如下来做到这一点：

    int total; // Total Minutes
    String time; // Input from keyboard

    final Scanner T = new Scanner(System.in);

    System.out.print("Enter the time in HH:MM :");
    time = T.next();

    boolean correctFormat = false;
    int hour = 0, minute = 0;

    while (!correctFormat) {
        correctFormat = true;

        if (time.length() != 5)
            correctFormat = false;
        else {
            try {
                hour = Integer.parseInt(time.substring(0, 2));
                minute = Integer.parseInt(time.substring(3, 5));
            } catch (NumberFormatException e) {
                correctFormat = false;
            }
            if (correctFormat) {
                if (hour >= 24 || hour < 0)
                    correctFormat = false;

                if (minute >= 60 || minute < 0)
                    correctFormat = false;
            }
        }
        if (!correctFormat) {
            System.out.print("Pleaase follow the format! Enter the time in HH:MM :");
            time = T.next();
        }
    }

    // Formula of the calculation
    total = hour * 60 + minute;

    // Display the final value
    System.out.println(time + " is " + total + " minutes.");